We report here on the observation of dislocation nucleation and glide in silicon nanoparticles, after phase transformation from diamond cubic to b-tin crystal structure, within the formed b-tin metallic phase region in atomistic simulations of indentation. The simulation results provide an explanation of the super-high hardness of silicon nanoparticles measured in experiments. By comparing the simulation results with experimental measurement of hardness, we are able to evaluate the performance of two widely used interatomic potential functions: Stillinger-Weber and Tersoff potentials. Through simulations, we have found a critical size of silicon nanoparticles where there is a change in deformation mechanisms, strength, and hardness. The effect of the applied strain rate on simulation results is also investigated.
The texture and microstructure of thin silver films in Ag/Ti bilayer structures have been characterized as a function of vacuum annealing temperature and time with the use of x-ray diffraction and transmission electron microscopy. A strong preexisting ͑111͒ texture in Ag films was further improved upon annealing as evidenced by an increased intensity and narrower distribution of the texture along the film normal. A new ͑200͒ texture component was generated after 600°C annealing; it however had a relatively low intensity when compared to the dominant ͑111͒ texture. No abnormal grain growth was observed in annealed Ag films. The texture evolution in all films appeared to complete within the first 15 min annealing, while the microstructure continued to change with additional annealing time. The roles of both surface energy and strain energy in the grain growth were evaluated. A model of the grain growth and texture evolution has been proposed to explain these observations.
The realization of advanced concept solar cells that circumvent assumptions inherent in the Shockley-Queisser limit depends strongly on a competition between carrier energy relaxation processes to the lattice and high energy processes that do useful work. Here we review the role of ultrafast carrier dynamics in the performance of such advanced concept devices, experimental results to date, and then present theoretical studies of such processes using ensemble Monte Carlo simulation of electrons, holes and phonons, with a particular focus on such processes in multi-quantum well systems, as well as III-V nanowires.
The texture of evaporated Ag films prepared on Ti or Cr underlayers before and after encapsulation process has been studied by x-ray diffraction. In addition, the stress state in self-encapsulated Ag/Ti structures has also been investigated using a “sin2 ψ” technique. Silver films deposited on Ti layers exhibit a strong 〈111〉 texture, which is in contrast to the nearly random orientation of Ag films on Cr underlayers. The minimization of interfacial energy with respect to lattice match can account for this underlayer dependence. After an encapsulation process involving Ti reactions in an ammonia ambient, the texture of Ag films in Ag/Ti bilayers is further enhanced. Highly textured Ag films may provide the basis for electromigration-resistant Ag metallization in integrated circuit devices. For the Ag/Ti bilayer structures, a low tensile stress of approximately 61 MPa arising from the nonequilibrium growth during the film deposition is present in the Ag films. This results in a lattice tension state in the film plane and a lattice compression state along the film normal. Thermal mismatch stress is produced by the encapsulation process at 600 °C. Most of this stress relaxes during the cooling stage and a residual tensile stress of ∼320 MPa in the film plane was determined.
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